1. Field of the Invention
The invention relates to the art of ferrous metallurgy, and namely to the design of a sintering machine, and is employed for making a sinter for blast furnaces, said sinter containing not more than 0.2 to 0.3% fines ranging in size from 5 to 0 mm.
The fines ranging in size from 5 to 0 mm, contained in the sinter, exert an influence upon gas dynamic resistance of a column of charge materials of the blast furnace, said resistance in turn influencing coke consumption and capacity of the blast furnace.
2. Prior Art
The quality of the sinter depends on a type of a sorting device employed in the sintering machine.
To sort the sinter in accordance with its size, it is possible to apply stationary bar screens, air classifiers, and vibrating screens.
Stationary bar screens have a low capacity caused by clogging slots of the bar field and by reducing the working area of the screen.
Prior art air classifiers are also characterized by a low capacity and by large overall dimensions, which features prevent their application in sintering machines since such an application would cause creation of a bulky sorting complex.
Known in the art is an air classifier (USSR Author's Certificate No. 473,532) comprising a frame, a receiving tray supported by a stationary shaft and a return spring, a system of levers, a diffuser, branch pipes provided with a movable wall member and a stationary wall member, said wall members forming slots whose profile is made in accordance with the Laval nozzle, a separation chamber provided with funnels for coarse and fine material, and a fan. Within the separation chamber there is mounted a distributor receiving device, a rotary partition member disposed between the funnels, and a device for purifying the air supplied to the fan from dust.
The above air classifier operates as follows.
A material to be classified is fed along the receiving tray to the distributor receiving device and thence into the zone of the separation chamber where the diffuser is disposed.
Under the action of a jet of the air being forced by the fan through the diffuser there occurs separation of the material into a fine fraction and a coarse fraction. The coarse fraction of the material flows into a funnel disposed close to the diffuser, while the fine fraction flows into the next funnel.
Ingress of the coarse fraction of the material into the funnel designed for the fine fraction is prevented by a rotary partition member mounted between the funnels, the size of openings provided in the partition member being less than that of the coarse fraction.
From the separation chamber the air is sucked by the fan through the device for purifying the air and is again directed into the diffuser.
In the case of variation of feed loading, the receiving tray rotates about the stationary shaft and, by means of the system of levers and the return spring, shifts the movable wall members of the branch pipes to or from the stationary wall member, thereby increasing or reducing a space provided therebetween. As a result, the speed of the air jet directed to the material to be separated is either increased or reduced. A required jet speed at a minimum air consumption is ensured due to a profile of the slot through which the air is passing, said slot having the form of the Laval nozzle.
The above described air classifier has a low effectiveness of classification of the material and a low carrying capcity, caused by inertia of the "receiving tray-branch pipes" system, and by the distributing device which does not influence the magnitude of the flow of a material being supplied therethrough into the separation chamber.
Thus, as the load on the receiving tray increases, the air speed also increases, while the material flow remains the same, since this flow is limited by the distributing device. The above fact results in an overblow, i.e. occurence of coarse particles within the funnel for the fine material. On the contrary, when the load on the receiving tray reduces, the air speed is too low to carry out the process, and the distributing device still distributes the material for some time into the separation chamber at the previous speed, thereby resulting in an underblow, i.e. fine particles appear within the funnel for the coarse material.
The air purifying device is also ineffective since it reduces the flow section of the separation chamber. The air speed increases sharply, thereby leading to entrainment of dust and to supply of this dust into the fan instead of settling it down. A closed system for feeding and removing the air results in accumulation of dust therewithin, in ejection of this dust into the atmosphere, and in rapid damage of the pipelines for feeding and removing the air due to high abrasive properties of said dust.
The slope of the rotary partition member is not adjusted with the variation of load on the receiving tray, which results in that the fine fraction gets into the coarse one.
In vibration screening, separation of fines ranging in size from 5 to 0 mm from the sinter is accomplished mainly in the lower layer of the sinter contacting directly with a bar screen, therefore the process of classification of the sinter should be carried out on several vibrating screens.
Moreover, the removal of fines from the sinter is impeded by the surface structure of coarse bits of sinter, which is characterized by the presence of extremely developed channels and macropores, wherein lie dust particles, fines and fragments.
The closest to the design of the present invention is a sintering machine (Kawamura Minour, Hasegawa Akira, Kawabe Masaguni, Koseya Shoichi, "Trans. Iron and Steel Inst. Jap.", 1974, 14, No. 3, pp. 208-216), comprising an assembly for loading a bed, an assembly for loading a charge, an ignition hearth, a sinter belt, an exhauster, a sinter breaker, an inclined chute, an air purifying device, a gas cleaning device, a system for cooling a sinter return and the bed, a collector, and a system for sorting the sinter, consisting of five vibrating screens mounted in series in a first row and in a second reserve row.
Laying a bed layer onto the sinter belt is ensured by the assembly for loading the bed, following which the charge is supplied thereover by the assmebly for loading the charge, said charge being ignited by the ignition hearth and subjected to sintering by sucking the air through the charge layer containing a fuel. The sinter thus obtained is crushed by the sinter breaker and is directed by the inclined chute to vibrating screens where separation of the sinter into a return and a suitable sinter takes place, both said fractions being cooled within the system for cooling the return and the sinter coolers respectively. The collector provides for removal, by means of the exhauster, of process gases from the layer being sintered into the gas cleaning device.
The above sintering machine makes it possible to obtain a sinter containing not more than 4 to 5% fines ranging in size from 5 to 0 mm, which is the world best index for quality of sinter. It should be noted, however, that the above sintering machine is excessively complicated and bulky since the total area of screens being utilized has reached 190 m.sup.2 as against 10 to 15 m.sup.2 when applying a conventional production process. Moreover, an increase in the number of sorting devices results in augmentation of material and labour consumption for their repair, service and use.
Residual content of fines ranging in size from 5 to 0 mm, which constitutes 4 to 5%, can be explained by deposition of dust particles and fragments within winding channels and macropores which are present in a sinter lump. Being of a small mass, these particles are easily transported by a coarse lump and do not participate in the process of sorting. For this reason, a further increase in the number of vibrating screens involved in the process of sorting the sinter will not result in decreasing the content of fines.